The automotive market recognizes the need to develop and produce cost-effective automotive transmissions with improved fuel efficiency and adequate launch performance. Also, to optimize shifting in a transmission, it is recognized that it is desirable to isolate launch and target gears during a gear shift. Constant Velocity Transmissions are known. Unfortunately, these transmission tend to be expensive. Transmissions with dual power inputs for odd and even gears are known. Some of these dual input transmission use manual transmission components. Unfortunately, the North American automotive market is dominated by automatic transmission and automatic transmission components, such as planetary gearsets, and it may be cost prohibitive to enact the production conversion needed to produce manual transmission components in sufficient quantities for dual input transmissions.
It is known to use planetary gearsets in a dual power input transmission. For example, U.S. Pat. Nos. 6,837,823 and 7,004,881 describe respective transmissions having a dual planetary gearset. Unfortunately, in both patents, the output of the transmission is connected only to a single planetary gearset in the dual planetary gearset, thus precluding the ability to isolate the launch and target gear or to have separate torque paths.
Switchable, one-way clutches are known, for example, as described in U.S. Pat. No. 6,409,001. Unfortunately, such clutches rely on extra mechanical components, such as pins, to implement the switching and locking functions.
Wet clutches are used in various torque transmittal applications, for example, in brakes to ground a planetary gearset in a transmission. For wet clutches, the characteristics of the fluid in the system affect the operation of the clutch, in particular, the friction coefficient. It is desirable to maintain a positive friction gradient during the operation of a clutch to prevent shuddering as the clutch closes. That is, the friction coefficient should decrease as slip speed decreases toward zero. Unfortunately, degradation of the fluid results in an undesirable negative friction gradient, that is, an increase in the friction coefficient as slip speed decreases toward zero, and subsequent shuddering during the closing of the brake. Replacing the fluid at more frequent intervals is not an attractive option due to the time and cost involved and the inconvenience to the user of the device housing the clutch, for example a vehicle with a transmission housing the clutch.
Thus, there is a long-felt need for a cost-effective dual torque path transmission using automatic transmission components such as planetary gearsets. There also is a long-felt need for a simpler switchable, one-way clutch controllable using elements already present in an application, for example, a transmission. Further, there is a long-felt need for a wet clutch able to minimize the impact of undesired changes in friction gradient.